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D. lanceolata, shells 153-169 µm long, nuclei 23-26 µm (Naardermeer, Netherlands)

Difflugia lanceolata Penard, 1890

Diagnosis: Shell clavate, elongate and composed of more or less flat siliceous angular particles arranged so that the sides appear polished and smooth. Fundus shaped like an ovigals arch. Aperture circular and often surrounded by an organic collar. Nucleus ovular, with small roundish nucleoli, some of them flattened against the nucleolar membrane. No zoochlorellae.

Penard (1902) described this species as follows: “The shell is always lanceolate, uncompressed, almost smooth, very regular in its contours; the shape is roughly that of a more or less elongated oak acorn. The fundus is almost always regularly rounded; more rarely there is a tendency to an ogival shape, more or less pronounced, or even, in very exceptional cases, to the formation of a terminal nipple. The shell is hyaline, thin, chitinoid, and always covered with flat, thin siliceous particles. Rarely, a few small stones are also noticed on the surface. Plasma is abundant, and always contains many small, colorless shiny grains, then, constantly also, pale starch grains, very small, not spherical, but elongated and curved. Zoochlorellae never present. The nucleus is spherical; its diameter is 28 µm on average; it is very pale, very beautiful, with a fine and frank membrane. The interior is filled with a nuclear juice of a light greenish blue, in which can be seen, especially on the surface, pale and delicate nucleoli, flattened, discoid, with tendency to a crescent shape. Between these nucleoli are embedded pale, rounded grains, much smaller, like dust. Pseudopods are large and few in number: most often only one or two are seen. The size generally varies between 140 and 160 µm.”

Dimensions: Penard (1902): Length 140-160 µm; nucleus ≈ 28 µm. My measurements 138-200 µm; nucleus 23-26 µm (n=3).

Ecology and distribution: Freshwater, several water types. I found it also in eutrophic water, in ditches between heavily fertilized farmland. Chardez (1978) found that “D. lanceolata and D. penardi are species which are sometimes found in limnosaprobic muds (…)”.

Remarks: Sometimes the fundus is a little asymmetrically pointed, but the clean outline of this species is the main distinguishing feature, though also specimens with rougher xenosomes are found.

Difflugia lanceolata
Difflugia lanceolata, with distinct organic collar – 138 µm
Difflugia lanceolata
Difflugia lanceolata
Difflugia lanceolata
Difflugia lanceolata
D. lanceolata, nuclei, three in DIC, one in Fluorescence (stained with Acridine Orange)
Difflugia lanceolata
Shells 145-170 µm long, all from the same sample, Den Treek, Amersfoort – Photos stacked
Difflugia lanceolata
Shells 154-174 µm long; the first two shells from Den Treek, the right one from the Laegieskamp. The second shell was photographed in DIC.
Difflugia lanceolata
Shells resp. 200, 185 and 130 µm. All three shells were found in a sample from a location near the city of Lemmer, Friesland.
Difflugia lanceolata
Drawing: Penard, in Faune Rhizopodique du Bassin du Léman, 1902
Difflugia lanceolata
D. lanceolata, slide 262-2-3 from the Pénard Collection in Geneva – Photographed by Thierry Arnet, as part of the Pénard project (https://creativecommons.org/licenses/by-sa/3.0/deed.en).
Difflugia lanceolata
D. lanceolata, slide 260-9-4 from the Pénard Collection in Geneva – Photographed by Thierry Arnet, as part of the Pénard project (https://creativecommons.org/licenses/by-sa/3.0/deed.en).
Difflugia lanceolata
D. lanceolata, slide 261-9-1 from the Pénard Collection in Geneva – Photographed by Thierry Arnet, as part of the Pénard project (https://creativecommons.org/licenses/by-sa/3.0/deed.en).
Difflugia lanceolata
This is an interesting collection of shells, collected from a piece of floating debris, from the bottom of a ditch in the Naardermeer nature reserve, April 2021. Many shells have the typical “lanceolata” shape, but others are pyriform or cylindrical and/or pointed or provided with a spine. Probably all of these shells belong to the same population, there are no clear boundaries. Larger shells resemble D. lacustris and smaller ones D. linearis and D. bryophila . The original description of D. oblonga also easily fits this group.
Difflugia lanceolata
Difflugia lanceolata, 156 µm
Difflugia lanceolata
Difflugia lanceolata, with parasite; nucleus 22 µm.
Difflugia lanceolata
Difflugia lanceolata
Difflugia lanceolata, shell 190 µm, nucleus 28 µm.

Remarks: In the spring of 2012 I had also an interesting sample from a small floating piece of debris, coming from the bottom of a shallow ditch along the Naardermeer. The sample contained a huge collection of shells, most empty, but the smaller ones were inhabited. While all shells were present in some cubic centimeters of debris, it is likely that they were all related.

Difflugia bryophila
This plate shows a number of shells from the sample, arranged, on scale, from small (65 µm) to large (195 µm). It shows the variation in shape. Some shells bear a spine, others have a rounded fundus or a slight constriction in the centre.
I measured the length of 469 shells. The results are given in the graph below. It is remarkable that there are at least two populations. One possibility is that there are smaller shells in spring and larger shells later in the year. That could explain that in my sample (spring) only smaller shells were inhabited. A second explanation could be that there are at least two different species, but these cannot be distinguished light microscopically.
Difflugia bryophila-lacustris
Graph Difflugia bryophila
This graph shows the correlation between length and width of the same 469 shells from the graph above.
Ferry Siemensma, created February 23, 2019; last modified August 09, 2021
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